ZFS Install Guide

Introduction

This tutorial will show you how to install Funtoo on ZFS (rootfs). This tutorial is meant to be an "overlay" over the Regular Funtoo Installation. Follow the normal installation and only use this guide for steps 2, 3, and 8.

Introduction to ZFS

Since ZFS is a new technology for Linux, it can be helpful to understand some of its benefits, particularly in comparison to BTRFS, another popular next-generation Linux filesystem:

On Linux, the ZFS code can be updated independently of the kernel to obtain the latest fixes. btrfs is exclusive to Linux and you need to build the latest kernel sources to get the latest fixes.

ZFS is supported on multiple platforms. The platforms with the best support are Solaris, FreeBSD and Linux. Other platforms with varying degrees of support are NetBSD, Mac OS X and Windows. btrfs is exclusive to Linux.

ZFS has the Adaptive Replacement Cache replacement algorithm while btrfs uses the Linux kernel's Last Recently Used replacement algorithm. The former often has an overwhelmingly superior hit rate, which means fewer disk accesses.

ZFS has the ZFS Intent Log and SLOG devices, which accelerates small synchronous write performance.

ZFS handles internal fragmentation gracefully, such that you can fill it until 100%. Internal fragmentation in btrfs can make btrfs think it is full at 10%. Btrfs has no automatic rebalancing code, so it requires a manual rebalance to correct it.

ZFS has raidz, which is like RAID 5/6 (or a hypothetical RAID 7 that supports 3 parity disks), except it does not suffer from the RAID write hole issue thanks to its use of CoW and a variable stripe size. btrfs gained integrated RAID 5/6 functionality in Linux 3.9. However, its implementation uses a stripe cache that can only partially mitigate the effect of the RAID write hole.

ZFS supports data deduplication, which is a memory hog and only works well for specialized workloads. btrfs has no equivalent.

ZFS datasets have a hierarchical namespace while btrfs subvolumes have a flat namespace.

ZFS has the ability to create virtual block devices called zvols in its namespace. btrfs has no equivalent and must rely on the loop device for this functionality, which is cumbersome.

The only area where btrfs is ahead of ZFS is in the area of small file
efficiency. btrfs supports a feature called block suballocation, which
enables it to store small files far more efficiently than ZFS. It is
possible to use another filesystem (e.g. reiserfs) on top of a ZFS zvol
to obtain similar benefits (with arguably better data integrity) when
dealing with many small files (e.g. the portage tree).

For a quick tour of ZFS and have a big picture of its common operations you can consult the page ZFS Fun.

Disclaimers

Warning

This guide is a work in progress. Expect some quirks.

Important

Since ZFS was really designed for 64 bit systems, we are only recommending and supporting 64 bit platforms and installations. We will not be supporting 32 bit platforms!

Downloading the ISO (With ZFS)

In order for us to install Funtoo on ZFS, you will need an environment that already provides the ZFS tools. Therefore we will download a customized version of System Rescue CD with ZFS included.

Booting the ISO

Warning

When booting into the ISO, Make sure that you select the "Alternate 64 bit kernel (altker64)". The ZFS modules have been built specifically for this kernel rather than the standard kernel. If you select a different kernel, you will get a fail to load module stack error message.

Creating partitions

There are two ways to partition your disk: You can use your entire drive and let ZFS automatically partition it for you, or you can do it manually.

We will be showing you how to partition it manually because if you partition it manually you get to create your own layout, you get to have your own separate /boot partition (Which is nice since not every bootloader supports booting from ZFS pools), and you get to boot into RAID10, RAID5 (RAIDZ) pools and any other layouts due to you having a separate /boot partition.

gdisk (GPT Style)

A Fresh Start:

First lets make sure that the disk is completely wiped from any previous disk labels and partitions.
We will also assume that /dev/sda is the target drive.

# sgdisk -Z /dev/sda

Warning

This is a destructive operation and the program will not ask you for confirmation! Make sure you really don't want anything on this disk.

Create the zfs datasets

We will now create some datasets. For this installation, we will create a small but future proof amount of datasets. We will have a dataset for the OS (/), and your swap. We will also show you how to create some optional datasets: /home, /var, /usr/src, and /usr/portage.

In Chroot

Sync your tree

# emerge --sync

Add filesystems to /etc/fstab

Before we continue to compile and or install our kernel in the next step, we will edit the /etc/fstab file because if we decide to install our kernel through portage, portage will need to know where our /boot is, so that it can place the files in there.

Kernel Configuration

...wip

Installing the ZFS userspace tools and kernel modules

Emerge sys-fs/zfs (package not on wiki - please add). This package will bring in sys-kernel/spl (package not on wiki - please add), and sys-fs/zfs-kmod (package not on wiki - please add) as its dependencies:

# emerge zfs

Check to make sure that the zfs tools are working. The zpool.cache file that you copied before should be displayed.

# zpool status
# zfs list

If everything worked, continue.

Create the initramfs

genkernel

Install genkernel and run it:

# emerge genkernel
You only need to add --luks if you used encryption
# genkernel --zfs --luks initramfs

Installing & Configuring the Bootloader

GRUB 2

# emerge grub

Now install grub to the drive itself (not a partition):

# grub-install /dev/sda

boot-update

boot-update comes as a dependency of grub2, so if you already installed grub, it's already on your system!

Genkernel

If your using genkernel you must add 'real_root=ZFS=<root>' and 'dozfs' to your params.
Example entry for /etc/boot.conf:

Create initial ZFS Snapshot

Continue to set up anything you need in terms of /etc configurations. Once you have everything the way you like it, take a snapshot of your system. You will be using this snapshot to revert back to this state if anything ever happens to your system down the road. The snapshots are cheap, and almost instant.

To take the snapshot of your system, type the following:

# zfs snapshot -r tank@install

To see if your snapshot was taken, type:

# zfs list -t snapshot

If your machine ever fails and you need to get back to this state, just type (This will only revert your / dataset while keeping the rest of your data intact):

# zfs rollback tank/funtoo/root@install

Important

For a detailed overview, presentation of ZFS' capabilities, as well as usage examples, please refer to the ZFS Fun page.

Troubleshooting

Starting from scratch

If your installation has gotten screwed up for whatever reason and you need a fresh restart, you can do the following from sysresccd to start fresh:

Destroy the pool and any snapshots and datasets it has
# zpool destroy -R -f tank
This deletes the files from /dev/sda1 so that even after we zap, recreating the drive in the exact sector
position and size will not give us access to the old files in this partition.
# mkfs.ext2 /dev/sda1
# sgdisk -Z /dev/sda